CONDITION OF THE SAINT PETER SANDS. 35] 



horizontal, barring some slight undulations due to fissures and faulting 

 lines. 



Lithologic Characters. — Owen says of this sandstone, "At most of the 

 localities where it has been observed it is remarkable for its whiteness."* 

 Tins white color is due to the condition of the surfaces of the grains; 

 I hey are worn simply to a dead finish — not polished, as can readily he 

 seen by immersing them in water, when they become limpid. Its white 

 color is its preeminent character throughout Minnesota. Locally it is 

 stained red, brown, pink and even green through the infiltration of ferric 

 oxide, the particular color being due to the quantity or condition of this 

 oxide. Nowhere is there enough to make a pronounced change in the 

 chemical composition of the rock. Another element of impurity in this 

 rock, particularly within the Saint Anthony area, is fine, white kaolin. 

 Sometimes there is sufficient to render quite turbid the water in a test- 

 tube in which a spoonful of the sand has been poured. Possibly the 

 presence of this argillaceous matter coating the smooth quartz grains 

 prevents the cementation which would convert a clean sand into a 

 quartzite.f 



In speaking further of its purity and fitness for glass-making, Owen 

 states that an analysis gave but two-tenths of one per cent of foreign 

 matter, which is alumina, with a trace of carbonate of lime. J < >ne of the 

 writers several years ago made an examination of the rock at Minneap- 

 olis and found 98.50 per cent silica and the balance made up chiefly of 

 alumina; and Professor Dodge, of the university of Minnesota, found 

 the iron oxide of this Minneapolis rock to amount to only 17 hundredths 

 of one per cent. Both samples were taken from the unstained layers, 

 since they were made in the interests of glass manufacture.^ 



Mr. Julius Hortvet has recently analyzed the fossiliferous sandstone of 

 south Saint Paul for this paper with the following result: 



Si < ). 99.78 per cent. 



Fe., 3 trace. 



Mg ( ) trace. 



Ca, Xa and K were detected by spectroscopic tests. This result is 

 almost identical with thai of Owen already cited. 



In texture this sandstone is somewhat coarser in its bottom layers 

 than in the middle and upper ones. This seems to be the case at Can- 

 non falls and Nbrthfiel'd, although nowhere was a conglomeratic texture 



Geol. Survey Wis., [a. and Minn., 1852, p. 69. 

 f A. Geikis says : "It is owing, no doubt, to the purely siliceous character of the grafhs thai the 

 blending of these »i(li the surrounding cement is so intimate thai the rock often assumes an 

 almost flinty homogeneous texture." Textbook of Geology, 1st i d., 1882, p. ijt. 

 J [bid, p. 69. 

 Bull. Minn. Acad. Nat. Sci., vol. iii. no. I p. L13. 



